In conjunction with bridges which are overhead structures that extend over roads, railways, obstacles or the like, repair works are undertaken for the reinforcement of bridge piers against seismic failure and obsolescent deterioration. Such repair works are commonly known as lining works and include RC lining, steel plate lining and fiber lining as the mainstream works. However, since most bridges or overhead structures are located in the outdoor environment, they are exposed to weathering including rain, snow and mist. In the prior art, less efforts have been made on the countermeasure against penetration of rain water. Insofar as the inventors know, application of sealants is the only one known countermeasure. The steel plate lining and fiber lining methods require cumbersome maintenance and management, and the RC lining method needs a long working time. The mortar spraying method is proposed as an improvement over these methods and considered attractive. The mortar spraying method, however, includes a plurality of cumbersome steps, for example, the thickness of sprayed mortar must be controlled via reinforcing steel guides or the like, and the cure is time consuming. Under the circumstances, if deterioration over time can be suppressed by taking a countermeasure against penetration of rain water, then some advantages are expected including an extension of the life of bridges and a reduction of the expense for maintenance and management. In the current practice of applying sealants, the surface to be applied must be dry. In case of bad weather like rain, snow or mist, workers must wait until the weather becomes fine and specifically until the wet surface becomes dry enough to accept the sealant.